We describe a patient who presented with a neutrophilic leukocytosis, normal karyotype, and IgA lambda multiple myeloma. One year after diagnosis she developed diffuse myelofibrosis as well as multiple lytic lesions of bone. Given the myeloproliferative features of her case, the clonality of her peripheral leukocytes was determined prior to treatment. Analysis of X-chromosome inactivation at the X-linked human androgen-receptor gene locus (HUMARA) proved that granulopoiesis was polyclonal. Subsequent treatment of the myeloma reversed with myelofibrosis and normalized her WBC count. This is the first case of multiple myeloma with myelofibrosis in which a concomitant clonal myeloproliferative disease was ruled out at a genetic level. The myeloproliferative features in this case are presumed to be induced by cytokines produced by the plasma cell clone.